The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing tools are used to process substrates such as semiconductor wafers. The processing often involves exposing the substrate in a processing chamber to vaporized precursor. For example only, processes such as chemical vapor deposition (CVD), plasma-enhanced CVD (PECVD), atomic layer deposition (ALD), plasma-enhanced ALD (PEALD) and fluorine free tungsten (FFW) expose the substrate to one or more vaporized precursors when depositing a layer on the substrate.
One approach for generating the vaporized precursor involves vaporizing a liquid precursor. It is difficult to vaporize liquid precursors with low vapor pressure (generally less than 1 Torr at room temperature) and high viscosity (>5 cP). Liquid precursors with low vapor pressure and high viscosity easily re-condense and cannot be vaporized using direct liquid injection since high viscosity liquids do not atomize easily. Also, liquid precursors that decompose at temperatures well below the boiling point are not suitable for being vaporized post atomization. Systems and methods for vaporizing precursors with low to medium vapor pressure typically include vapor draw, bubblers or flow over a single surface of liquid inside an ampoule. Other options use atomizers and vaporizers. However, for low to moderate flow rates of precursors, vaporizers are not ideal.
Standard bubblers are able to saturate a carrier gas with precursor. However, the carrier gas flow rate is often limited by splashing concerns. Single surface flow-over systems where the carrier gas flows into an ampoule but not into the liquid are able to increase total pressure in the ampoule such that the vaporized precursor can flow from the ampoule to the processing chamber. However, the carrier gas does not saturate with the vapor and the amount of vaporized precursor that can be transported to the processing chamber is relatively low.